Plant Communities of the World 2.6'j 



The system here given accords with physiognomic-ecologic 

 considerations. The innate ecology is seized in order to give 

 expression to sociologic gradation, to prograding stages of organ- 

 ization. In this the system of communities is quite analogous 

 to the systems of plants, which also are built up in progressive 

 stages of organization. At the bottom of the list we put the 

 floating communities, of very loose union. The least stable are 

 those floating in the air, then those floating in the water, then 

 those suspended in the ice. Also, small primitive organisms in 

 and on the soil may be called floating. Above stands the stone 

 and wood vegetation, still mosdy one-layered without root com- 

 petition; above these, in turn, the rocky grounds and other 

 deserts with some open vegetation — open, it may be, on account 

 of the rocky ground, the mobility of the ground (dunes, screes, 

 alluvials), the cold climate (open tundra), the dry climate. 

 Higher stand the closed communities: first, the swampy ones 

 — submersed aquatic, emersed aquatic, moors; then the few- 

 layered communities on land — tall herbage, meadows, prairies, 

 short-grass communities. The highest organized types are the 

 several-layered woody communities of shrubs, and especially of 

 trees, forming the complicated forest communities, differing 

 according to the climates. 



For the purpose of a synopsis, it will be well to follow up these 

 larger formation-classes, their ecology, morphology, and distri- 

 bution. Of associations and other smaller unities, only examples 

 can be given.* 



i.Pltwiisilvae: Rain forests. — ^Pluviisilvae are forests rich in 

 epiphytes whose dominant plants consist of evergreen and often 



* A more detailed account of them will be found in my Pflanzengesellschaften 

 der Erde (Verlag Hans Huber, Bern; 1930), where also a multicolored world map 

 shows the distribution of climatic formation-classes. Brockmann-Jerosch, who 

 did the map, has published a large wall map of the formation-classes (Justus 

 Perthes, Gotha). 



